EM - Escola de Minas

URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/6

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A Escola de Minas de Ouro Preto foi fundada pelo cientista Claude Henri Gorceix e inaugurada em 12 de outubro de 1876.

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Heat treatment effects on the hardness and wear behavior of laser-welded AISI40 martensitic steel plates.
(2021) Gonçalves, Karina Aparecida Martins Barcelos; Faria, Geraldo Lúcio de; Siqueira, Rafael Humberto Mota de; Oliveira, Tarcísio Reis de; Lima, Milton Sérgio Fernandes de
The use of laser beams for joining materials has grown along with the need to weld more challenging materials such as martensitic steels. In this work, an AISI 420 martensitic steel plate was autogeneously welded using a fiber laser. The process parameters were 2000 W power and weld speed of 16 mm/s with the focus on the plate surface. Before welding, the plates were prepared in two conditions, tempered, or annealed, and tempering was performed at temperatures of 300°C, 400°C, 500°C, and 700°C after welding. The finite element analysis and dilatometric tests allowed to determine the phase transformations of this steel under development by the company Aperam. The observed microstructure varies according to the initial state of the plate and subsequent heat treatments. The hardness of the fusion and heat-affected zones varied according to the samples. The welded sample in the tempered state softened moderately due to the reheating of the laser beam. In the case of the annealed sample, the hardness of the molten zone was the highest obtained. This high hardness was reflected by a high resistance to wear by reciprocal sliding in the annealed case, compared to the other conditions. The fusion zone generally proved to be much more resistant to wear than the base material.
Effect of PWHT on laser-welded duplex stainless steel : the effects of postweld heat treatments on the microstructure, tensile behavior, and corrosion resistance of laser-welded duplex stainless steel were investigated.
(2020) Magalhaes, Aparecida Silva; Magalhães, Charles Henrique Xavier Morais; Lima, Milton Sérgio Fernandes de; Alves, Juliane Ribeiro da Cruz; Godefroid, Leonardo Barbosa; Bertazzoli, Rodnei; Faria, Geraldo Lúcio de
The welded joints of duplex stainless steels (DSSs) have been widely used in petrochemical, nuclear, pulp, and paper industries. Welds require a good, superficial finishing and a combination of mechanical and corrosion properties in these types of high-quality, demanding applications. Even though laser welding promotes narrow weld beads and a small heataffected zone, when it is applied to DSSs, it can produce dangerous microstructural discontinuities. In this context, the effects of subsequent heat treatments on the microstructure, corrosion resistance, microhardness, and tensile properties of DSS laser-welded joints are investigated. In this study, samples of UNS S32304 DSS were submitted to two different conditions of laser welding. Subsequently, the plates submitted to the best welding condition were subjected to isothermal heat treatments at different temperatures (850°, 950°, 1050°, and 1150°C) for 10 min. Then they were microstructurally characterized. Phase fraction measurements and microhardness tests were performed. Based on the obtained results, postweld heat-treated samples at 1150°C, which is the best condition, were subjected to corrosion and tensile tests. It was possible to conclude the corrosion properties of the welded joint were significantly improved after the heat treatment. However, the mechanical behavior was strongly influenced by the presence of volumetric discontinuities and intermetallic compounds, which considerably deteriorated the mechanical strength of the material.
Weldability and mechanical behavior of laser-welded TRIP 750 steel sheets.
(2020) Gonçalves, Thais Soares; Faria, Geraldo Lúcio de; Siqueira, Rafael Humberto Mota de; Lima, Milton Sérgio Fernandes de
Transformation-induced plasticity steels have been developed and widely applied in the automotive and aerospace industries. They exhibit ductility and mechanical strength associated with a high formability due to their complex microstructure of bainiteassociated pro-eutectoid ferrite and significant retained austenite fractions. The weldability of these steels is limited by the high content of alloying elements in the composition, causing the thermal cycle to modify the carefully designed microstructure, which in turn generates unsatisfactory weld mechanical properties. Laser welding has a relatively low thermal input, and, therefore, a narrow heat-affected zone is obtained. As known, the literature had not been definitively reported the microstructural features of the fusion and the heat-affected zones after laser welding of TRIP steels in conjunction with their mechanical behavior. The aim of the present work is to characterize the microstructure and mechanical behavior of laser-welded TRIP steel after uniaxial tensile and Erichsen formability tests. The coupons of TRIP 750 steel sheets were subjected to different laser welding conditions in order to analyze their impact on the microstructure, hardness, and mechanical strength of the material. After some preliminary tests, the laser power was fixed at 900 W and the weld speed fixed at 50 mm/s as the best choice of operating parameters. Under these conditions, the fusion zone was almost completely martensitic, while the heat-affected zone had a mixture of ferrite and martensite. The martensite transformation is corroborated by finite elements analyses as the cooling rate was 4200 °C/s for material at martensite start temperature. The average hardness of the fusion zone was 530 HV and the heat-affected zone was 550 HV, compared with 270 HVof the base material. In terms of mechanical behavior, the tensile strength of the welded coupons was found to reach 740 MPa and the ductility reached 22% in uniform deformation. The Erichsen index for the welded sheets attained 15 mm for a load of 48.5 kN, similar with the non-welded base material. Both in the case of the uniaxial tensile testing and in the Erichsen testing, the fracture occurred in the base material away from the weld, showing a good toughness of the welded component.
Effect of different forms of application of a laser surface treatment on fatigue crack growth of an AA6013-T4 aluminum alloy.
(2019) Gonçalves, C. M.; Godefroid, Leonardo Barbosa; Lima, Milton Sérgio Fernandes de; Sampaio, N. P.
This work analyzes the effect of surface-localized laser heating treatment on the fatigue crack growth (FCG) rate on region II of the sigmoidal da/dN 3 DK curve of an aerospace-grade AA6013-T4 aluminum alloy sheet with 1.3 mm thickness. The influence on microstructure changes is also evaluated. Aiming to improve the FCG resistance without changing the mechanical behavior of the alloy, a Yb:fiber laser beam is defocused to generate a laser spot diameter of 2 mm, using 200 W power and a laser speed of 2 mm/s. Two laser lines are applied over fatigue C(T) specimens in two different forms: on only one and on both lateral specimen surfaces. Guinier–Preston zones, dispersoids and coarse constituent particles are found on the base material. On the heat-treated material, the same precipitates and also b¢ and Q¢ precipitates are found. These microstructural variations due to the laser thermal cycle, together with the presence of induced compressive residual stresses, improved the fatigue behavior of the material. The FCG retardation is optimized when two laser lines were applied on both lateral surfaces of the specimen.
Computational fluid dynamics and experimental analysis of a coated stainless steel gas turbine blade.
(2019) Souza, Leandro Augusto; Leal, Elisângela Martins; Costa, Adilson Rodrigues da; Lima, Milton Sérgio Fernandes de
This work Aims to analyze, through computational fluid dynamics (Cfd) with the concept of conjugate heat transfer (Cht), the effect of the Thermal Barrier coating and the cooling systemon an Austenitic Stainless steel blade in order to Evaluate the Temperature Behavior of the Material. Although this Steel has a Lower cost compared to Super ALLOYS, it has Similar Properties, Such as the Thermal Expansion Coefficient, chemical Affinity and Melting point. this Evaluation used Ansys® Cfx Software ot Solve the Numerical Problem. the Systemis Validated by Comparing the computational Results to an Experiment. Gas Turbine Blades have a low weight and an Elevated cost. this cost came Mainly form both the Material used and the Sophisticated coating and cooling Method. Thermal Barrier Coatings Associated to a cooling System are Employed on gas Turbine Blades to Increase the Lifetime of the Blade and the gas Turbine Performance. the study Indicates that the Thermal Barrier coating and ahe cooling System were Efficient At Reducing the Temperature of the Metallic Substrate By 160°C. this can Indicated that Stainless steel Blades can be used in gas turbines where the Metallic Temperature limit was not be reached.
Characterization of phase transformations and microstructural changes in an API 5CT L80 steel grade during ni alloy laser cladding.
(2018) Faria, Geraldo Lúcio de; Paula, Jorge Magalhães Ávila de; Lima, Milton Sérgio Fernandes de
The superficial coatings in micro-alloyed steel pipes has been a pointed way to decrease the corrosion problems in oil and gas industry. However, little emphasis has been given to the substrate. The effects of the deposition method on the steel microstructure and properties are still not well described. In this context, this work studied the effect of Ni superalloys clads on the phase transformations, microstructure and hardness of the heat-affected zone (HAZ) of an API steel. The underestimate of the HAZ might be dangerous, since, despite the coating good corrosion performance, the substrate HAZ may present a weak region, which may lead to an in-service coating tearing. In this work, Inconel 625 and Hastelloy C276 superalloys were clad on the steel surface by a laser deposition. Dilatometry, optical and scanning electron microscopy, and computational simulation were applied. The studied steel was originally constituted by tempered martensite. The austentizing temperature had a strong influence on the austenite grain size and on the steel CCT diagram. Due to that, the laser superalloy deposits promoted a complex HAZ, where grain growth occurred. A post-cladding heat treatment was proposed to homogenize the steel microstructure and to decrease the hardness gradient at the superalloy-steel interface.
A comparative study of the heat input during laser welding of aeronautical aluminum alloy AA6013-T4.
(2018) Coelho, Bruno Nazário; Lima, Milton Sérgio Fernandes de; Carvalho, Sheila Medeiros de; Costa, Adilson Rodrigues da
The heat input is the amount of energy supplied per unit length of the welded workpiece. In this study, the effect of two different heat inputs in laser beam welding of a high strength aluminum alloy AA6013-T4 was evaluated from macrostructural and microstructural points of view. The experiments were performed using a continuous wave 2 kW Yb-fiber laser with 100 μm spot size on the upper surface of the workpiece. Keeping the heat input at a given level, 13 or 30 J/mm, the laser power was changed from 650 W to 2 kW and the welding speed from 33 to 150 mm/s. In the condition of higher heat input 30 J/mm it was possible to obtain both cutting and welding processes. For 13 J/mm, welding processes were obtained in conduction and keyhole modes. The equiaxed grain fraction changed with changing speed for the same heat input. The laser processing induced a decrease in the hardness of the weld bead of about 25% due to the solubilization of the precipitates. The estimated absorptivities of the laser beam in the liquid aluminum changed largely with experimental conditions, from 4.6% to 10.5%, being the most significant source of error in measuring the real amount of energy absorbed in the process. For the same heat input the macrostructure of the welded surfaces, i.e., humps and dropouts, changed as well. All these facts indicate that the heat input is not a convenient method to parameterize the laser beam welding parameters aiming the same weld features.
Evaluation of hydrogen-Induced cracking resistance of the In625 laser coating system on a C-Mn steel substrate.
(2017) Trindade, Vicente Braz; Almeida, Natália Chaves; Cândido, Luiz Cláudio; Faria, Geraldo Lúcio de; Lima, Milton Sérgio Fernandes de
The corrosion of C-Mn steels in the presence of hydrogen sulfide (H2S) represents a significant challenge to oil production and natural gas treatment facilities. The failure mechanism induced by hydrogen-induced cracking (HIC) in a Inconel 625 coating / C-Mn steel has not been extensively investigated in the past. In the present work, an API 5CT steel was coated with In625 alloy using laser cladding and the HIC resistance of different regions, such as the coating surface, the substrate and HAZ, were evaluated. SEM observations illustrated that all HIC cracks were formed at the hard HAZ after 96h of exposure. No HIC cracks were observed in the substrate and the In625 coating after the same exposure duration. Pitting was recorded in the substrate caused by non-metallic inclusion dissolving.
Laser cladding and thermal spray coatings on steel pipe serving the oil and gas industry.
(2016) Almeida, Natália Chaves; Cândido, Luiz Cláudio; Faria, Geraldo Lúcio de; Lima, Milton Sérgio Fernandes de; Trindade, Vicente Braz
Different coating systems were characterized using a commercial API 5CT steel grade L80 type 1, which is commonly used in the oil and gas industry. Two Ni-based alloys and one Co-based alloy were deposited by laser cladding. Two coatings were deposited (Ni-based alloy and a composite W-C/Co-base) by means of thermal spray process. It has been shown the presence of a hard heat affected zone (HAZ) in the substrate for the as-laser deposited coating. The main explanation for this HAZ is devoted to the heat gradient causing a gradient on the prior austenite grain size and consequently different martensite hardness along the HAZ. For the thermal sprayed coatings, no HAZ was formed due to low heat input process. All the studied coating systems seem to be very interesting for different technically demanding applications, such as, stress sulfide corrosion and wear resistance.
A multi-objective green UAV routing problem.
(2017) Coelho, Bruno Nazário; Coelho, Vitor Nazário; Coelho, Igor Machado; Ochi, Luiz Satoru; Koochaksaraei, Roozbeh Haghnazar; Zuidema, Demetrius; Lima, Milton Sérgio Fernandes de; Costa, Adilson Rodrigues da
This paper introduces an Unmanned Aerial Vehicle (UAV) heterogeneous fleet routing problem, dealing with vehicles limited autonomy by considering multiple charging stations and respecting operational re- quirements. A green routing problem is designed for overcoming difficulties that exist as a result of lim- ited vehicle driving range. Due to the large amount of drones emerging in the society, UAVs use and efficiency should be optimized. In particular, these kinds of vehicles have been recently used for deliver- ing and collecting products. Here, we design a new real-time routing problem, in which different types of drones can collect and deliver packages. These aerial vehicles are able to collect more than one deliver- able at the same time if it fits their maximum capacity. Inspired by a multi-criteria view of real systems, seven different objective functions are considered and sought to be minimized using a Mixed-Integer Lin- ear Programming (MILP) model solved by a matheuristic algorithm. The latter filters the non-dominated solutions from the pool of solutions found in the branch-and-bound optimization tree, using a black-box dynamic search algorithm. A case of study, considering a bi-layer scenario, is presented in order to val- idate the proposal, which showed to be able to provide good quality solutions for supporting decision making.

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